This invention relates generally to plating and more particularly to the catalytic surface preparation of substrates prior to electroless metal plating.
In the electroless plating of metal films onto the surfaces of various substrates which are non-conductive, it is conventional to treat the surface to be plated to activate it so that a layer of metal can be deposited by chemical deposition. The catalytic treatment acts to catalyze and/or accelerate the depositing of the metal film on the surface and causes the film to form a continuous and adherent layer.
In the past, various sensitizing compositions and processes have been employed. One well known technique is to utilize a plurality of baths in which the substrate is first immersed in a stannous chloride solution followed by immersion in an acidic palladium chloride solution to form an activating deposit of palladium on the substrate. Single sensitizing baths of colloidal dispersions of palladium and tin as described, for example, in U.S. Pat. No. 3,011,920; or soluble complexes of palladium-tin-chloride prepared by heating aqueous acid mixtures of the metal salts as is described, for example, in U.S. Pat. No. 3,682,671 have also been employed.
It has been found that it is difficult to form adherent coatings on certain substrates, particularly glasses.